"""
Exposes several methods for transmitting cyclic messages.
The main entry point to these classes should be through
:meth:`can.BusABC.send_periodic`.
"""
from typing import Optional, Sequence, Tuple, Union, Callable, TYPE_CHECKING
from can import typechecking
if TYPE_CHECKING:
from can.bus import BusABC
from can.message import Message
import abc
import logging
import threading
import time
# try to import win32event for event-based cyclic send task (needs the pywin32 package)
try:
import win32event
HAS_EVENTS = True
except ImportError:
HAS_EVENTS = False
log = logging.getLogger("can.bcm")
[docs]class CyclicTask(abc.ABC):
"""
Abstract Base for all cyclic tasks.
"""
[docs] @abc.abstractmethod
def stop(self) -> None:
"""Cancel this periodic task.
:raises can.CanError:
If stop is called on an already stopped task.
"""
[docs]class CyclicSendTaskABC(CyclicTask):
"""
Message send task with defined period
"""
def __init__(
self, messages: Union[Sequence[Message], Message], period: float
) -> None:
"""
:param messages:
The messages to be sent periodically.
:param period: The rate in seconds at which to send the messages.
:raises ValueError: If the given messages are invalid
"""
messages = self._check_and_convert_messages(messages)
# Take the Arbitration ID of the first element
self.arbitration_id = messages[0].arbitration_id
self.period = period
self.messages = messages
@staticmethod
def _check_and_convert_messages(
messages: Union[Sequence[Message], Message]
) -> Tuple[Message, ...]:
"""Helper function to convert a Message or Sequence of messages into a
tuple, and raises an error when the given value is invalid.
Performs error checking to ensure that all Messages have the same
arbitration ID and channel.
Should be called when the cyclic task is initialized.
:raises ValueError: If the given messages are invalid
"""
if not isinstance(messages, (list, tuple)):
if isinstance(messages, Message):
messages = [messages]
else:
raise ValueError("Must be either a list, tuple, or a Message")
if not messages:
raise ValueError("Must be at least a list or tuple of length 1")
messages = tuple(messages)
all_same_id = all(
message.arbitration_id == messages[0].arbitration_id for message in messages
)
if not all_same_id:
raise ValueError("All Arbitration IDs should be the same")
all_same_channel = all(
message.channel == messages[0].channel for message in messages
)
if not all_same_channel:
raise ValueError("All Channel IDs should be the same")
return messages
[docs]class LimitedDurationCyclicSendTaskABC(CyclicSendTaskABC):
def __init__(
self,
messages: Union[Sequence[Message], Message],
period: float,
duration: Optional[float],
) -> None:
"""Message send task with a defined duration and period.
:param messages:
The messages to be sent periodically.
:param period: The rate in seconds at which to send the messages.
:param duration:
Approximate duration in seconds to continue sending messages. If
no duration is provided, the task will continue indefinitely.
:raises ValueError: If the given messages are invalid
"""
super().__init__(messages, period)
self.duration = duration
[docs]class RestartableCyclicTaskABC(CyclicSendTaskABC):
"""Adds support for restarting a stopped cyclic task"""
[docs] @abc.abstractmethod
def start(self) -> None:
"""Restart a stopped periodic task."""
[docs]class ModifiableCyclicTaskABC(CyclicSendTaskABC):
"""Adds support for modifying a periodic message"""
def _check_modified_messages(self, messages: Tuple[Message, ...]) -> None:
"""Helper function to perform error checking when modifying the data in
the cyclic task.
Performs error checking to ensure the arbitration ID and the number of
cyclic messages hasn't changed.
Should be called when modify_data is called in the cyclic task.
:raises ValueError: If the given messages are invalid
"""
if len(self.messages) != len(messages):
raise ValueError(
"The number of new cyclic messages to be sent must be equal to "
"the number of messages originally specified for this task"
)
if self.arbitration_id != messages[0].arbitration_id:
raise ValueError(
"The arbitration ID of new cyclic messages cannot be changed "
"from when the task was created"
)
[docs] def modify_data(self, messages: Union[Sequence[Message], Message]) -> None:
"""Update the contents of the periodically sent messages, without
altering the timing.
:param messages:
The messages with the new :attr:`Message.data`.
Note: The arbitration ID cannot be changed.
Note: The number of new cyclic messages to be sent must be equal
to the original number of messages originally specified for this
task.
:raises ValueError: If the given messages are invalid
"""
messages = self._check_and_convert_messages(messages)
self._check_modified_messages(messages)
self.messages = messages
[docs]class MultiRateCyclicSendTaskABC(CyclicSendTaskABC):
"""A Cyclic send task that supports switches send frequency after a set time."""
def __init__(
self,
channel: typechecking.Channel,
messages: Union[Sequence[Message], Message],
count: int, # pylint: disable=unused-argument
initial_period: float, # pylint: disable=unused-argument
subsequent_period: float,
) -> None:
"""
Transmits a message `count` times at `initial_period` then continues to
transmit messages at `subsequent_period`.
:param channel: See interface specific documentation.
:param messages:
:param count:
:param initial_period:
:param subsequent_period:
:raises ValueError: If the given messages are invalid
"""
super().__init__(messages, subsequent_period)
self._channel = channel
class ThreadBasedCyclicSendTask(
ModifiableCyclicTaskABC, LimitedDurationCyclicSendTaskABC, RestartableCyclicTaskABC
):
"""Fallback cyclic send task using daemon thread."""
def __init__(
self,
bus: "BusABC",
lock: threading.Lock,
messages: Union[Sequence[Message], Message],
period: float,
duration: Optional[float] = None,
on_error: Optional[Callable[[Exception], bool]] = None,
) -> None:
"""Transmits `messages` with a `period` seconds for `duration` seconds on a `bus`.
The `on_error` is called if any error happens on `bus` while sending `messages`.
If `on_error` present, and returns ``False`` when invoked, thread is
stopped immediately, otherwise, thread continuously tries to send `messages`
ignoring errors on a `bus`. Absence of `on_error` means that thread exits immediately
on error.
:param on_error: The callable that accepts an exception if any
error happened on a `bus` while sending `messages`,
it shall return either ``True`` or ``False`` depending
on desired behaviour of `ThreadBasedCyclicSendTask`.
:raises ValueError: If the given messages are invalid
"""
super().__init__(messages, period, duration)
self.bus = bus
self.send_lock = lock
self.stopped = True
self.thread: Optional[threading.Thread] = None
self.end_time: Optional[float] = (
time.perf_counter() + duration if duration else None
)
self.on_error = on_error
if HAS_EVENTS:
self.period_ms = int(round(period * 1000, 0))
self.event = win32event.CreateWaitableTimer(None, False, None)
self.start()
def stop(self) -> None:
if HAS_EVENTS:
win32event.CancelWaitableTimer(self.event.handle)
self.stopped = True
def start(self) -> None:
self.stopped = False
if self.thread is None or not self.thread.is_alive():
name = f"Cyclic send task for 0x{self.messages[0].arbitration_id:X}"
self.thread = threading.Thread(target=self._run, name=name)
self.thread.daemon = True
if HAS_EVENTS:
win32event.SetWaitableTimer(
self.event.handle, 0, self.period_ms, None, None, False
)
self.thread.start()
def _run(self) -> None:
msg_index = 0
while not self.stopped:
# Prevent calling bus.send from multiple threads
with self.send_lock:
started = time.perf_counter()
try:
self.bus.send(self.messages[msg_index])
except Exception as exc: # pylint: disable=broad-except
log.exception(exc)
if self.on_error:
if not self.on_error(exc):
break
else:
break
if self.end_time is not None and time.perf_counter() >= self.end_time:
break
msg_index = (msg_index + 1) % len(self.messages)
if HAS_EVENTS:
win32event.WaitForSingleObject(self.event.handle, self.period_ms)
else:
# Compensate for the time it takes to send the message
delay = self.period - (time.perf_counter() - started)
time.sleep(max(0.0, delay))